Control system



May 9, 1933. B. M. MILLS 1,908,163

CONTROL SYSTEM Filed Dec. 10, 1931 Fig. 2. Pig. 3.

Fig. 4. Fig. 5.

Invefitorn- Bruce mfflills, /MM

H is Attorney.

v 20 lel to supply the necessary power for hoistcitation tor the generator 12 and the motor Patented May 9, 1933 UNITED STATES BRUCE M. MILLS, OF SCHENECTADY, IJEW' YQRI'T, ASSIGNOE TO GENERAL ELECTRIC COMPANY, A GGEPGBATIQH GE NEW 103K CONTROL My invention relates to variable voltage For a more complete understanding of my control systems of the lVard-Leonard type invention, reference should now be had to and more particularly to a plurality of genthe awing in which Fig. 1 diagrammaticalerat-ors arranged under certain conditions trates a control system embodying my jointly to supply a single load and under ntion; Figs. 2 and 3 illustrate in simpli- 55 other conditions to supply individual loads, form the c mnections or the field circuit and has for an object the provision of a of the generators shown in Fig. l for difiersimplified system of this character having cnt c1 nlitions of operation; while Figs. 4 improved operating characteristics. and 5 illustrate in simplified form a modifica- While my invention is broadly applicable tion of my inven ion as applied to the field 60 to a variety of uses, it is particlarly advancircuits of a pair of generators, the field tageous for use in oil well drilling equipwindings ot which are arranged to be conment. In oil well drilling, the skill of the letted in parallel. operator plays an important part and it is Referring to the drawing, Ihave shown my essential that he shall know the response that invention in one term as applied to the Vardcan be obtained for a given setting of the Leonard drives 10 and 11. A generator 12 field rheostat. For example, if it is desired is connected in local circuit with a motor 18, to operate the hoisting drive, it is desirable the separately excited field windings 14 and to connect two or more generators in paral- 15 being arranged respectively to supply exing. For other operations each generator 13. Similarly, a generator 17 is connected in may be connected to an individual load,therelocal circuit with a motor 18, the field windfore a further object of my invention is to ings 19 20 being arranged to supply exprovide for the individual operation of the citation for the generator and motor. As

2 several generators so that their volt-ampere shown the field windings 1e and 19 are respeccharacteristics shall be substantially the tively excited by means of an exciter 22 prosame as when the generators are jointly supvided with self-excited field winding 23, and plying power to a load. an exciter 2 lsimilarly provid d with a self- In carrying out my invention in one form excited winding 25. It will be understood,

thereof, I provide for maintaining the resistof course, that the field windings of the ance of the separately excited field circuits of generators may be excited through an auxa plurality of generators constant for a given iliary source oi direct current supply instead setting of the field rheostat, whether the genof the exciters it it is so desired. erators are supplying current to their respec- Assuming that it is desired to operate the tive motors with individual control by sepa- WardLeonard sets 10 and 11 with each genrate rheostats or whether they are connected erator independently controlled by the field jointly to supply power to a single load with rheostats 26 and 2?, the single pole double joint control from one of the rheostats. throw switch 28 will be operated to its left- More specifically, for a pair of generators I hand position, thereby completing an enerprovide an auxiliary resistance in the field gizing circuit for the contactor 29. This cir- 0 circuit of each generator having a value cuit may be traced from the positive side of which is equivalent to the resistance of the the exciter 22, conductor 30, control switch field winding ot the other generator. When 28, conductor 31, operating coil 32 of the conthe generators are connected jointly to suptactor and by conductor 33 to the other ply power to a single drive. I provide for inside of the excit-er armature. The contactor serting the field winding of one generator in 9 is thereupon operated to its closed posiplace of the auxiliary resistance, thereby obtion, thereby connecting the field winding 14 taining the same volt-ampere characteristics in series with a fixed resistance 34, equal to on the generator for a given setting of the the resistance of the field winding 19, and afield rheostat. field rheostat 26. Similar vthrough the lower contacts of the contactor 29 the field winding 19 of the generator 17 is connected in series with a fixed resistance 35 equal to the resistance of the field winding 14, a field rheostat 27 and the armature of the exciter 24. It will be understood that the voltage of the generators 12 and 17 may be independently controlled by adjusting the field rheostats 26 and 27 which in practice are usually reversing rheostats. It will also be understood that other auxiliary resistances may be inserted in the field circuits for purposes well known to the art. For this condition of operation the motors 13 and 18 may be respectively geared to separate loads such as to the hoisting mechanism and to a mud pump of an oil well drilling equipment.

Should it be desired, however, to operate the generators 12 and 17 jointly to supply power to a single load with a single control rheostat, the switch 28 will be operated to its right-hand position.

The closing of the switch 28 completes an energizing circuit for the contactor 38. This circuit may be traced from the positive side of the exciter 22 by conductor 30, control switch 28, conductor 39, operating coil 40 of the contactor 38 and by conductor 33 to the other side of the exciter 22. The contactor 38 is thereupon operated to its closed position to connect the field winding 19 in series with the field winding 14, the armature of exciter 22 and field rheostat 26, but leaving the resistances 34 and 35 out of this field circuit. It will be understood that the voltage of the generators 12 and 17 may thus be jointly and simultaneously controlled by adjusting the field rheostat 26.

For this condition of operation the motors 13 and 18 are mechanically connected to a single drive such as the hoisting mechanism of an oil well drilling equipment by means of suitable gearing or the like (not shown). It is to be understood, however, that a single hoisting motor could be used, it having a volt-ampere rating equal to the sum of the volt-ampere ratings of the generators so that the generators could be electrically connected with their armature circuits in parallel or series jointly to supply power to such single hoisting motor.

Therefore, for the two conditions of operation described, for a given setting of the field rheostats the voltage of the generators for a given value of armature current will be the same whether the generators are separately controlled or whether they are controlled by the single rheostat 26. This may be clearly seen by referring to Figs. 2 and 3. In Fig. 2 it will be observed that the field winding 14 is connected in series with the resistance 34 and the field rheostat 26 while the field winding 19 is connected in series with the resistance 35 and the field rheostat 27. These connections represent the first condition with each generator independently controlled by the respective rheostats 26 and 27.

For the second condition of operation, however, as represented by Fig. 3, the field windings 14 and 19 are connected in series with the field rheostat 26. Inasmuch as the resistance of the winding 19 is equal to the resistance 34, it will be observed that the series resistance of the circuit in Fig. 3 remains the same as the series resistances of each of the separate field circuits shown in Fig. 2. Therefore, for a given ampere load per generator, the same response is obtained from the generators 12 and 17 for a given setting of the field rheostat 26 as is obtained with individual control of each generator with the same setting of the field rheostats 26 and 27. In other words, the o erating characteristics of each generator wit joint operation of the generators are the same as with individual operation.

Now that the principle of my invention has been explained, its application to various combinations of connections of field circuits will be obvious to those skilled in the art. For example, if it be desired to take into account the time constants introduced due to the inductance of the field windings, it will be understood that instead of employing the non-inductive resistances 34 and 35, impedances may be used, each of which has the same reactance and resistance as the res ective field windings 14 and 19. By so emp oying impedances, it will be seen that the time constantsof the field circuits will remain substantially the same Whether the generators are jointly controlled by a single rheostat or whether they are independently controlled by separate rheostats.

Referring now to Fig. 4, I have shown an impedance 50 connected in parallel with the field winding 14, and a second impedance 51 connected in parallel with the field windin 19. As before, the field rheostats 26 and serve to control the excitation of the generator field windings when the generators are to be separately con-trolled However, when the generators are connectedjointly tosupply a single load, the field winding 19 is connected in parallel with the field winding 14, the field rheostat 26 controlling the excitation of these field windin While I ave shown particular embodiments of my invention, it will be understood, of course, that I do not wish to be limited thereto, since many modifications may be made, and I therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. In a system of distribution, a plurality of generators having substantially similar operating characteristics, separately excited field windings therefor, a single control circuit including more than one of said field windings for one condition of operation, a single control means included in said circuit for simultaneously controlling the energization of more than one of said field windings for said one condition, additional control means for said field windings, means for connecting each of said field windings in individual circuits for another condition of operation each circuit including one of said control means, and means included in each individual circuit for rendering each individual circuit the electrical equivalent of said single control circuit.

2. In a system of distribution, a pair of similar generators, each of which is provided with a separately excited field winding, a rheostat, connections for connecting said windings in series with said rheostat for the joint control of the excitation of said generators, a second rheostat, a pair of resistances each saving the same resistance as one of said field windings, and connections -tor connecting each field winding in circuit with a rheostat and a resistance so that each generator may be separately controlled through a circuit having the same equivalent resistance as for said joint operation of said generators.

3. In a system of distribution, a plurality of generators having substantially similar operating characteristics, separately excited field windings therefor, a rheostat for each of said generators, connections for connecting said windings in series with each other and with one of said rheostats for the joint control of the excitation of said generators, a plurality of resistances and means for connecting each of said field windings in series with one of said rheostats and sutlicient of said resistances so that the resistance of each field circuit is equal to the resistance of said windings connected in series with one of said field rheostats.

4. In a system of distribution, a plurality of generators having substantially similar operating characteristics, separately excited field windings therefor, a rheostat for each of said generators, connections for connecting said windings in parallel with each other, and in series with one of said rheostats for the joint control of the excitation of said generators, a plurality of resistances, and means for connecting each of said field windings in series with one of said rheostats and in parallel with sufiicient of said resistances so that the equivalent resistance of each field circuit is equal to the resistance of said windings when connected in parallel.

5. In combination, a plurality of dynamoelectric machines having substantially similar operating characteristics, a separately ex- 3 cited field winding for each machine, a control rlieostat operable to control the excitation produced by said field windings, connections for connecting said field windings in circuit with said control rheostat for simultaneous control of the excitation of said machines, additional control rheostats, connections for connecting each of said field windings in circuit with one of said control rheo stats, impedance means included in circuit with each or" said rheostates for producing the same change in energization of a field winding for a given operation of its control rheostats as for a corresponding operation of said first-mentioned control rheostat.

6. In combination, a plurality 01" variable voltage drives each of which includes a generator and a motor, afield winding for each generator, connections for connecting said field windings in circuit with each other, a single control means for controlling simultaneously the energization of said field windings for one condition of operation, individ ual control means for separately controlling the energization of said field windings, connections for connecting each of said individual control means in circuit with a single field winding for another condition or" operation, and means included in circuit with each of said individual control means for producing the same change in energization of a field winding for a given operation of an individual control means as for a corresponding operation of said single control means.

7. In a system of distribution, a pair of similar generators, each of which is provided with a separately excited field winding, a rheostat, connections for connecting said windings in series with said rh ostat for the joint control of the excitation of said generators, a second rheostat, a pair of impedances each having the same impedance as one of said field windings and connections for connecting each field winding in circuit with a rheostat and an impedance so that each gerierator may be separately controlled through a circuit having the same equivalent impedance as for said joint operation of said generators.

In witness whereof, I have hereunto set my hand.

BRUCE M. MILLS. 

